95-GHz Front-End Receiving Multichip Module on Multilayer LCP Substrate for Passive Millimeter-Wave Imaging

In this paper, directional filters (DFs) are first proposed to improve the stability of multichip modules (MCMs), and a new integration approach between microstrip line on liquid crystal polymer (LCP) substrate and electrooptic (EO) modulator on lithium niobate substrate is presented, together enabling an EO front-end receiving MCM at 95 GHz for passive millimeter-wave (mmW) imaging with large distributed aperture. The DFs can efficiently pick the spectrum of interest with low reflection and drop the undesired out-of-band power to the additional ports, thus reducing the possibility of oscillation. With the above and some other integration and packaging technologies, the multilayer LCP-based MCM achieves a high gain of more than 63 dB, a 3-dB bandwidth of 4.7 GHz centered at 95 GHz, and a low noise figure of less than 6 dB within this spectrum, which was characterized using both radio frequency and optical measurement approaches. The packaged MCM has been successfully utilized in passive mmW imaging and may find lots of applications in other wireless systems.